Lloyd Alter
DCL
Earlier this season we presented a series of low tech tips for reducing the cost of cooling your home. One I missed was the attic fan. In more temperate parts of the country,just moving the air and having good ventilation could eliminate the need for AC much of the time.
Attic fans used to be noisy and act as a big leaky hole in the ceiling in winter. But they are getting pretty sophisticated, like this Airscape unit, which has automatic dampers that seal it up tight. It has low speed, quiet fans that were designed for computers; you would thik that it wouldn't do very much. But Airscape explains:
While on the surface it may seem like more CFM equals better cooling, it turns out that old-style fans, with their enormous flow rates, were unnecessary overkill. The main function of a whole house fan is not simply to replace hot air with cooler air—it is to cool down the entire structure by drawing off the heat. And this takes time. Even with very high air flow—say 5000 CFM—your house can only shed pent-up heat at a limited rate. So there is a point of diminishing returns that needs to be considered against noise. You reach a point where you could double the airflow, which would quadruple the noise, yet only speed up the cooling process by 20 or 30%. So what?s really effective is slower flow over a longer period with quiet operation.
Attic fans are one of those forgotten technologies that have been replaced by energy and carbon intensive alternatives like air conditioning. It is great seeing that they are coming back.
